2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/5517Statistical properties of gas absorption in high redshift quasars such as power spectrum and bispectrum allow one to determine the evolution of structure over the redshift range 2<z<4. Sloan Digital Sky Survey (SDSS) will measure around 10,000 quasar spectra in this redshift range and will allow one to determine the growth factor with a few percent accuracy. This allows one to extend the studies of dark energy to higher redshift and determine the presence of dark energy if Omega_de>0.1-0.2 at z>2. In combination with low redshift studies one can place useful limits on the time evolution of the equation of state.5 pages, to appear in proceedings of the XVIII'th IAP Colloquium `On the Nature of Dark Energy', IAP ParisAstrophysicstext